How to add carbon fiber to cars?
You might look at the cycles material car thread on Blenderartists and see if you can adapt soe of the materials from there - then you could just assign as needed to parts of the mesh directly, or use a black and white image uv mapped to the mesh as a stencil between node trees, combining materials into one tree. https://blenderartists.org/t/car-paint-materials-iridescent-layers-carbon-fiber-leather/536803/108?u=craig_jones